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Interfacial thermal conductance (ITC) quantifies heat transport across material–fluid interfaces. It is a property of crucial importance to study heat transfer processes at both macro- and nanoscales. Therefore, it is essential to accurately model the specific interactions between solids and liquids. Here, we investigate the thermal conductance of gold–water interfaces using polarizable and non-polarizable models. Both models have been fitted to reproduce the interfacial tension of the gold–water interface, but they predict significantly different ITCs. We demonstrate that the treatment of polarization using Drude-like models, widely employed in molecular simulations, leads to a coupling of the solid and liquid vibrational modes that give rise to a significant overestimation of the ITCs. We analyze the dependence of the vibrational coupling with the mass of the Drude particle and propose a solution to the artificial enhancement of the ITC, preserving at the same time the polarization response of the solid. Based on our calculations, we estimate ITCs of 200 MW/(m2 K) for the water–gold interface. This magnitude is comparable to that reported recently for gold–water interfaces [279 ± 16 MW/(m2 K)] using atomic fluctuating charges to account for the polarization contribution. [ABSTRACT FROM AUTHOR]

The Interfacial Thermal Conductance (ITC) is a fundamental property of materials and has particular relevance at the nanoscale. The ITC quantifies the thermal resistance between materials of different compositions or between fluids in contact with materials. Furthermore, the ITC determines the rate of cooling/heating of the materials and the temperature drop across the interface. Here, we propose a method to compute local ITCs and temperature drops of nanoparticle–fluid interfaces. Our approach resolves the ITC at the atomic level using the atomic coordinates of the nanomaterial as nodes to compute local thermal transport properties. We obtain high-resolution descriptions of the interfacial thermal transport by combining the atomistic nodal approach, computational geometry techniques, and "computational farming" using non-equilibrium molecular dynamics simulations. We use our method to investigate the ITC of nanoparticle–fluid interfaces as a function of the nanoparticle size and geometry, targeting experimentally relevant structures of gold nanoparticles: capped octagonal rods, cuboctahedrons, decahedrons, rhombic dodecahedrons, cubes, icosahedrons, truncated octahedrons, octahedrons, and spheres. We show that the ITC of these very different geometries varies significantly in different regions of the nanoparticle, increasing generally in the order face < edge < vertex. We show that the ITC of these complex geometries can be accurately described in terms of the local coordination number of the atoms in the nanoparticle surface. Nanoparticle geometries with lower surface coordination numbers feature higher ITCs, and the ITC generally increases with the decreasing particle size. [ABSTRACT FROM AUTHOR]

Janus particles (JPs) are a special kind of colloids that incorporate two hemispheres with distinct physical properties. These particles feature a complex phase behavior, and they can be propelled with light by heating them anisotropically when one of the hemispheres is metallic. It has been shown that JPs can be oriented by a homogeneous thermal field. We show using multiscale simulations and theory that the internal mass gradient of the JPs can enhance and even reverse the relative orientation of the particle with the thermal field. This effect is due to a coupling of the internal anisotropy of the particle with the heat flux. Our results help rationalize previous experimental observations and open a route to control the behavior of JPs by exploiting the synergy of particle–fluid interactions and particle internal mass composition. [ABSTRACT FROM AUTHOR]

Non-equilibrium molecular dynamics simulations have expanded our ability to investigate interfacial thermal transport and quantify the interfacial thermal conductance (ITC) across solid and fluid interfaces. NEMD studies have highlighted the importance of interfacial degrees of freedom and the need to include effects beyond traditional theoretical methods that rely on bulk properties. NEMD simulations often use explicit hot and cold thermostats to set up thermal gradients. We analyse here the impact of the thermostat on the calculated ITC of the gold-water interface. We employ a polarisable model for gold based on Drude oscillators. We show that the 'local' Langevin thermostat modifies the vibrational density of states of the polarisable solid, resulting in ITCs that depend very strongly on the damping constant of the thermostat. We report an increase of the ITC of up to 40% for short damping times. Damping times longer than the characteristic heat flux relaxation time of the solid lead to converging ITCs. In contrast, the ITCs obtained with global canonical velocity rescale thermostats are independent of the damping time but lead to a break of equipartition for Drude particles. Setting individual thermostats for the core and shell sites in the Drude particle solves this problem. [ABSTRACT FROM AUTHOR]